10
DigiBoard Intelligent Serial Communications Boards
DIP Switch Settings
PC/Xi boards have two banks of DIP switches labeled DS1 and DS2 (see Figure
2 for the location of the DIP switches). DS1 has eleven switches which are used
to set the board’s I/O port address and the starting address of the board’s dual-
ported memory. DS2 is an eight-position switch that specifies which Interrupt
Request (IRQ) line to use.
Consult your software installation instructions for recommended address
and IRQ selections.
Memory Start Address—DS1, Switches 1-8
PC/Xi boards communicate with the host computer through dual-ported (or
“shared”) memory. This memory resides on the PC/Xi board, but is directly
accessible to the host computer as if it was the host’s own memory. The PC/Xi
board’s dual-ported memory must be mapped into an empty block of host
address space. Since the board’s entire dual-ported memory is accessible to the
host, the size of this empty block must correspond to the size of the board’s
memory (64K, 128K, 256K or 512K). 64K and 128K boards may be mapped
into the area below 1 megabyte, above the system RAM, and all boards may be
mapped into high memory (between the 14th and 16th megabyte).
PC/Xi memory can be switched on or off by setting or resetting a bit in the
board’s I/O port. This permits multiple PC/Xi boards to occupy the same block
of memory addresses. This is an especially valuable feature when installing
boards below 1 megabyte where memory address space is limited. Most
DigiBoard device drivers support this “memory stacking” concept (an exception
is the PC-MOS driver).
Switches 1-8 of DIP switch bank DS1 can be set to indicate the start of any 64K
block of memory in the first 16 megabytes (from 000000h to FF0000h). In
practice, very few of the possible addresses are actually used. DigiBoard device
drivers utilize only 15 memory start addresses (not all drivers support all 15
addresses—consult your device driver installation guide for specifics). The 15
commonly used addresses are given on the following pages, along with a
pictorial representation of the corresponding DIP switch settings.
